Hardening 5G Network Registration: An Analysis of ECIES Profiles and SHNIP

5G networks promise unprecedented capacity and latency, yet user-plane privacy during registration remains at risk. We present the first implementation-level evaluation of all three 3GPP registration profiles—Null, Profile A (Curve25519-ECIES), and Profile B (secp256r1-ECIES)—and introduce SHNIP, a lightweight extension that encrypts the Home-Network Identifier (HNI). Using FREE5GC (v3.3.0) and UERANSIM (v3.2.6) on synchronized testbeds, we measure latency, CPU load, memory use, and resilience to three attacks: IMSI catching, SUCI probing, and Invalid-Curve exploitation.Results show Profile B blocks the Invalid-Curve flaw seen in many Profile A deployments but adds ∼12% processing and 5 ms latency. SHNIP restores HNI privacy atop either profile with only 73 μs UE computation—2.1× faster than prior art. AVISPA verification confirms secrecy and authentication, while live attack scripts show 99.9% mitigation of SUCI probing.Our study delivers the first holistic performance–security trade-off map for 5G registration and offers operators a deploy-today hardening path.